Generally, a tactile switch is to switch circuits by a slight touch. It has been widely used as a part of various modernized electronic products due to its simple operation and accuracy in switching circuits and its simple structure.
Recently, the tactile switch has been used in mobile communication devices such as cellular phones, and various up-to-date electronic personal devices such laptop computers, handy cassettes, MP3 players, etc. which tend to be more and more miniaturized. Following this tendency, a PCB type tactile switch having a smaller size, lighter weight and less thickness than the conventional tactile switch has been developed.
One conventional PCB type tactile switch is shown in FIG. 1 in its sectional view. It comprises:
an insulating member (10) made of nonconducting material in the shape of a thin plate;
a upper pattern (20) made of conducting material, provided on the insulating member (10), and including a central contact (21), an external contact (23) and a short circuit part (22) to electrically short-circuit between the central contact (21) and the external contact (23);
a lower pattern (30) made of conducting material and provided under the insulating member (10);
a metal dome (40) made of elastic and conducting metallic material and having a convex center and a circumferential end which secures on the external contact (23) of the upper pattern (20), wherein the convex center is protruded in the shape of a dome away from the central contact (21), and is pressed by an external pressure to come into contact with the central contact (21) to apply electricity;
a cover layer (50) made of nonconducting substances to fix the metal dome (40) on top of the upper pattern (20);
a through hole (60) formed by perforating the upper pattern (20), the insulating member (10) and the lower pattern (30) to provide a shelter for the air in the metal dome (40) in clicking the metal dome (40); and
a solder mask (70) covering a bottom surface of the lower pattern (30) with nonconducting substances, except for bottom parts of the lower pattern (30) which require soldering.
Therefore, if a user presses a central part of the metal dome (40), as the circumferential end of the metal dome (40) has already been contacted to the external contact (23), the convex center of the metal dome (40) comes into contact with the central contact (21), which drives a circuit connected to any corner of the lower pattern (30) by soldering or applies operating signals to the circuit.
In the above conventional tactile switch, when the metal dome (40) is slightly pressed to apply the electric current to the circuit or apply operating signals, the bottom surface of the convex center of the metal dome (40) comes into contact around the central part of the upper pattern (20).
In this case, however, since the conventional tactile switch was manufactured in a small and compact size in order to be adopted for ultralight and very thin electronic parts, the convex center of the metal dome (40) was formed low. Thus, in the conventional tactile switch shown in FIG. 1, wherein the central contact (21) was as high as the external contact (23), if the metal dome (40) had been clicked, the user could feel it only minutely.
Therefore, the user could rarely detect the contact of the metal dome (40) with the central contact (21), which might cause the user to click further or once more, which in turn might cause wrong operation of the electronic parts and entire electronic products.
In addition, the through hole (60), which provides shelter for the inside air of the metal dome (40) in clicking the metal dome (40), was formed by the process of perforation by means of a drill. However, since the perforation of the through hole (60) of a very small diameter should be done on the very thin and small tactile switch, it required a lot of skill and accuracy in order to reduce the inferiority of goods.
Further, since the volume of the through hole (60) was not enough to hold the air under the metal dome (40), it was difficult to expect that all of the inside air under the metal dome (40) could be retained in the through hole (60). Thus, the sensibility over the clicking deteriorated.
Furthermore, since the through hole (60) was formed by perforating the upper pattern (20), the insulating member (10) and the lower pattern (30), lead could be introduced into the through hole (60), during the process of soldering at the corners of the tactile switch for connection to the circuit.
Therefore, in order to prevent the inflow of the solder into the through hole (60) and to provide insulation as well, the solder mask (70) was provided under the lower pattern (30) by a method of printing. However, since the through hole (60) could not be covered with ink completely by printing the solder mask (70), it was necessary to perform the printing 2 or 3 times, which resulted in the increase of manufacturing time and costs.
Also, although the through hole (60) had been blocked by ink through many times of printing, the effect of blocking was not complete, thus resulting in inferior products and deterioration of reliability of products.